Process in joining

ABSTRACT

In a process in roller folding a folding roller is moved against a workpiece. The urging force of the folding roller against the workpiece is resilient, and the folding roller moves in a path along the workpiece by means of a movement device provided with a control system. The urging force is sensed by a sensor, which is integral in or included in the movement device, and the output signal of the sensor is fed to the control system.

TECHNICAL FIELD

The present invention relates to a process in joining, more precisely aprocess in roll folding, where a folding roller is moved, with resilientcompressive force, against a workpiece in a path along it by means of amovement device provided with a control system.

BACKGROUND ART

In the joining together of two sheet metal parts in such contexts wherethe demands on surface finish are high, folding or roller folding isoften employed as a superior alternative to welding. Roller foldingproceeds such that one of the workpieces is given an edge portionprojecting out over the other workpiece, the edge portion being foldedin over the other workpiece and urged against it so that the edge of theother workpiece will be accommodated between the first workpiece and itsfolded-over edge portion. During this working cycle, the workpieces reston and are positionally fixed in relation to a bed which thereby willdefine the form of the finished fold.

For the above-mentioned folding over of the edge portion of the firstworkpiece, use is made of a roller which is displaced in thelongitudinal direction of the edge portion. Before the foldingoperation, the first workpiece has its edge portion projectingapproximately at right angles or at least transversely directed inrelation to the plane of the portion of the workpiece lying inside theedge portion. The roller is then generally moved in three differentsteps along the edge portion so that this, in a first folding step, isbent at approximately 30° and in a second folding step an additionalapproximately 30°. The subsequent and last folding step is the crucialstep when the surface finish of the workpiece is determined.

The two first folding steps may be carried out without any majorrequirements on precision in the relative positions between the foldingroller and the edge portion of the workpiece. This also applies to thecompression force which prevails between the folding roller and the edgeportion.

On the other hand, as regards the final step in the folding operation,extremely high demands on the precision of movement are placed, as wellas demands on a certain resilience capability in the roller. Inaddition, the compression force from the roller on the edge portionresting on the bed must often vary along the length of the edge portionso that, for example, in a tightly bent “corner region” of theworkpiece, the compression force must be reduced since the edge portionmust be considerably narrower in such a curved region.

EP 577 876 shows, with reference to FIGS. 7 and 8; and 9 and 10,respectively, apparatuses for roller folding. Common to both of theseembodiments is that an industrial robot carries an end effector orfolding head with two main components, where the one main component isconnected to the industrial robot while the other main component ismovable in relation to the first towards and away from the workpiece,The construction includes a servo apparatus by means of which the mutualposition of the two main components can be controlled in order therebyto vary or realise a resilient force in the abutment of the foldingroller against the workpiece.

The described embodiments may be feared to suffer from serious drawbacksas regards the precision in the abutment force of the folding roller andits path of movement because of the movable interconnection of the maincomponents in the folding head. Further, the folding head will,naturally, be extremely complicated and expensive.

Further drawbacks in the prior art technology reside in the fact thatthe apparatus in principle comprises two different movement mechanisms,one for displacing the folding head and one for displacing the foldingroller in the folding head. This implies that there are two sources ofdefective precision both as regards the compression force and accuracyin the path of movement of the roller.

ACCOUNT OF THE INVENTION

The present invention has for its object to formulate the processintimated by way of introduction such that the drawbacks inherent inprior art methods and apparatuses are obviated. In particular, thepresent invention has for its object to realise a process which may bereduced into practice without the employment of complicated andexpensive specialist equipment. Further, the present invention has forits object to realise a process which affords precision advantagescompared with prior art technology.

SOLUTION

The object forming the basis of the present invention will be attainedif the process intimated by way of introduction is characterised in thatthe resilience is generated by means of the movement device.

As a result of this feature, advantages will above all be afforded asregards simplicity in the equipment.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will now be described in greater detailhereinbelow, with particular reference to the accompanying Drawings. Inthe accompanying Drawings:

FIG. 1 is a perspective view of a folding head, mounted on an industrialrobot, intended to be employed for carrying the process into effect;

FIG. 2 is a partial section through a workpiece, the bed on which theworkpiece rests and a folding roller; and

FIG. 3 shows a lower portion of a modified folding head seen in thedirection according to the arrow C in FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT

The present invention will be described hereinbelow by way of example asapplied to an industrial robot. Naturally however, it may be applied inany other type of movement device or manipulator which is provided witha control system and which may realise the requisite relative movementpattern between a workpiece and a folding roller. Thus, the termmovement device should be given such a broad interpretation as also toinclude an apparatus which displaces a workpiece in relation to afixedly disposed folding roller, as well as apparatuses in which boththe workpiece and the folding roller move.

In FIG. 1 broken lines intimate a movement device or manipulator 1included in an industrial robot, the manipulator being that part of theindustrial robot which is movable along extremely complicated movementpaths and which serves for securing such end effectors or equipment asthe robot is to handle. Reference numerals 2 and 3 relate to first andsecond support members, support members in which the first or uppersupport member 2 is secured in the manipulator 1 of the robot by meansof suitable rapid coupling devices or bolt unions. The second or lowersupport member 3 supports, on each side, a folding roller 4 which isrotatably journalled in relation to the second support member and whichis rotary about a common axis 5. The folding rollers 4 are intended tobe in contact with and urge against an edge portion 10 on the workpiece12 which rests on a bed 13 (FIG. 2) and which is to be folded. Thus, thefolding roller is to move along a folding path.

The second support member 3 is movable in relation to the first supportmember 2 and, in particular, is pivotal in relation thereto about asecond axis 6 which is located a distance from the first axis 5 and theanchorage of the first support member 2 in the manipulator 1. Thisimplies that the second support member 3 may execute a pendulum pivotalmotion about the second axis 6, whereby the folding roller 4 may becaused to move towards and away from the edge portion 10 of theworkpiece.

The pivotal capability of the second support member 3 in relation to thefirst support member 2 is achieved in that the second support member isaccommodated between two lugs, of which only the lug 9 is shown in theFigure. A bearing shaft 11 extends through the two lugs, and defines thesecond pivot axis 6. The movement region of the second support member 3is restricted by the presence of a locking pin 14 which extends throughboth the lugs and through an arcuate curved recess in the second member3.

Between the two support members, there is disposed a rubber bellows 15which has an inlet 16 for air.

By the supply of air under pressure to the interior of the bellows, thebellows may be caused to function as a spring whereby the folding roller4 may be held resiliently urged against the workpiece 12.

However, it is also possible to increase the pressure in the bellows 15to such a level that the second support member 3 is locked in abutmentagainst the locking pin 14. In this state, the folding roller 4 isrigidly interconnected to the manipulator 1 of the industrial robot and,as a result, slavishly follows its movements.

It will be apparent from the foregoing that in those operational stateswhere the bellows has such high pressure that no movement between thefolding roller and the manipulator can occur, the folding roller couldjust as well be directly connected to the manipulator by theintermediary of a totally rigid connecting portion 17 (FIG. 2).

In the production of the workpiece 2, there is documented a line alongthe edge portion 10, the line being represented by the point 18 in FIG.2. This line along the periphery of the workpiece 12 is described incomputer files which are transferred to the control system in theindustrial robot. As a result, the robot becomes aware of the path whichis to be followed by the folding roller 4 on execution of a foldingcycle.

In order to localise the folding roller 4 in a particular manner inrelation to the line 18, a circumference line 19 is defined on thefolding roller and this circumference line is intimated in FIG. 2 by thepoint 19. By displacement of the circumference line 19 in relation tothe line 18 in response to material dimensions, folding width etc.,which is carried out by the employment of the control system of therobot, the desired mutual position may be achieved between the foldingroller and the edge portion 10 along the entire circumference of theworkpiece. The folding roller 4 can therefore be caused to follow thedesired folding path along the edge portion 10.

Another method of informing the control system of the industrial robotas to the desired folding path could be to allow a specific,narrow-edged sensor roller to follow and scan either the edge portion 10or a portion of the bed 13 located proximal the edge portion. By suchscanning, information may be transferred to the control system of theindustrial robot as to the path which the folding roller 4 issubsequently to follow in operation.

When a folding operation, and in particular its final phase, issubsequently to be carried out, correction must take place of the pathof the folding roller 4 in relation to the desired path programmed intothe robot, if the final result is to be that desired. These correctionsinclude variations of the abutment force of the folding roller againstthe workpiece 12 along the folding path, resilient spring movements inthe folding roller, etc.

The resilience which the robot according to the present inventionrealises may be passive or active.

The passive resilience is achieved by means of a spring element such asa helical spring, a torsion spring, a resilient rubber element, a gasspring etc., and requires no sensing of the abutment of the roller 4against the workpiece.

The active resilience is based on the concept that the abutment force ofthe roller 4 against the workpiece can be sensed by means of a sensor. Aforce generating device then urges the roller 4 more or less forciblyagainst the workpiece 12 in response to the output signal from thesensor so that the abutment force of the roller is kept at the desiredlevel.

In FIG. 2, the edge portion 10 is approximately projecting at a rightangle from the workpiece 12, and it should be observed that a secondworkpiece which is to be folded together with the workpiece 12 has beenomitted from the Figure.

In a first step in a folding cycle, the edge portion 10 is folded fromthe position illustrated by solid lines in FIG. 2 and is, in thisinstance, bent of the order of 30° inwards over the major part of theworkpiece 12 to a position which is illustrated by the broken line 20.The precision requirements during this first step in the folding cycleare low, for which reason the folding roller 4 may be kept rigid andimmobile in relation to the manipulator 1.

A second phase in the folding cycle is carried out when the edge portionis folded from the position illustrated by the broken line 20 to a newposition which is approximately illustrated by the broken line 21. Alsoduring this second step in the folding cycle, the requirements onprecision are low, both as regards the relative positioning between thefolding roller and the edge portion 10, as well as the abutment pressurefrom the folding roller against the edge portion. Consequently, alsoduring this second step, the folding roller 4 may be rigid and immobilein relation to the manipulator 1.

With a folding head according to FIG. 1, this implies that the twoabove-described steps in the folding process are carried out with suchhigh pressure in the bellows 15 that the lower support member 3 ispositionally fixed as a result of its urging against the locking pin 14realised by the bellows 15.

In the completion of the final step in a folding cycle, i.e. foldingover of the edge portion 10 from the position illustrated by means ofthe broken line 21 to a position approximately parallel with the mainpart of the workpiece 12 and in abutment against the second workpiece(not shown in FIG. 2), the requirements on precision, resilience andpower control are considerable.

In the final step in the folding cycle, i.e. the final folding, thefolding roller 4 is moved with a resilient urging force against theworkpiece 12 in a path along it. In order to compensate for suchinaccuracies in the path of movement which may possibly occur, it isessential that the folding roller 4 be permitted to spring in adirection towards and away from the edge portion 10. According to thepresent invention, this resilient function is realised in the industrialrobot. In such instance, the urging force of the folding roller 4against the edge portion 10 is sensed by means of a sensor which isintegrated in or included in the industrial robot. The output signalfrom this sensor is fed to the control system of the industrial robot sothat the industrial robot in itself, with its own movement devices, mayrealise the necessary resilience capability.

In one embodiment of the invention, that sensor which is employed formeasuring the abutment force of the folding roller against the workpiece12 is one or more of the drive motors included in the robot. This ispossible by sensing of the current which, at constant voltage, is fed tothe drive motors.

In another embodiment of the present invention, use is made of aspecific sensor which is positively placed between the folding roller 4and the power generating devices of the robot, i.e. its drive motors. Inone embodiment, this sensor is placed at the interface between thefolding head and the manipulator 1.

However, in one embodiment according to FIG. 1, the bellows 15 may alsobe employed as a sensor for emitting a signal to the control system ofthe robot, which thereby controls the drive motors of the robot in sucha manner that the requisite resilience is achieved. If the bellows isgiven so high an inner pressure that, in principle, it no longerfunctions as a spring but has not yet urged the second support member 3to the stop position against the locking pin 14, and if its inlet 16 isshut off, the inner pressure in the bellows 15 can be sensed andemployed as an input signal to the control system of the robot.

FIG. 3 shows a modified folding head which is designed, at least duringthe final folding, to offer even better precision. The folding head has,in addition to the folding roller 4, a guide roller 22 which is designedto follow a guide path 23 on the bed 13. In the illustrated embodiment,the guide roller 22 has an axis of rotation 24 running in the verticaldirection of the folding head and approximately parallel to thedirection in which the folding roller 4 moves in its resilient movementtowards and away from the workpiece during the final folding. Theillustrated orientation of the guide path 23 and the guide roller 22entail that the folding roller 4 will be guided extremely accurately inthe lateral direction of the fold which is in the process of beingproduced.

In the embodiment according to FIG. 3 the guide roller 22 may have arunning path with a coating of a resiliently yieldable or elasticmaterial such as a plastic or rubber material. Alternatively, suchmaterial may be disposed on the guide path 23.

What is claimed is:
 1. A process for folding a workpiece comprising thesteps of providing a folding roller: defining a first path along an edgeportion of the workpiece and recording this path in computer means ofmovement device means; applying a resilient urging force to the foldingroller by movement device means for moving the folding roller againstthe workpiece along the edge portion of the workpiece; defining a secondpath along a circumference line on the folding roller; sensing theresilient urging force by a sensor means; generating an output signalfrom the sensor means in response to the sensed resilient urging force;and feeding the output signal to the movement device means to keep thefirst and the second paths in a redetermined relationship to oneanother.
 2. The process as claimed in claim 1, wherein the sensor meanscomprises drive means included in the movement device means.
 3. Theprocess as claimed in claim 1, wherein the sensor means positivelydisposed between the folding roller and the movement device means. 4.The process as claimed in claim 1, wherein the folding roller, at leastduring a final step of a folding cycle, is guided in a lateral directionwith respect to the fold, wherein a guide roller follows the path on abed on which the workpiece rests.